Nanotechnologies are the science and business of manipulating matter at the atomic scale. Materials produced with the aid of various kinds of nanotechnologies are starting to be used in many areas of everyday life such as cosmetics, clothing fabrics, sports equipment, paints, packaging, food, etc. and has been used for some time as for instance catalysts in many important industrial processes. In the future we will no doubt see many more application of nanomaterials in general and of nanomaterials involving noble metals in particular.
Colloidal gold has been successfully used as a therapy for rheumatoid arthritis. An in vitro experiment has shown that the combination of microwave radiation and colloidal gold can destroy the beta-amyloid fibrils and plaque which are associated with Alzheimer's disease. Gold nanoparticles are being investigated as carriers for drugs such as Paclitaxel. In cancer research, colloidal gold can be used to target tumors and provide detection using SERS, Surface Enhanced Raman Spectroscopy in vivo.
Samsung home appliances, such as refrigerators or air conditioners, come with a silver nano coating to their inner surfaces which provide an overall anti-bacterial and anti-fungal effect. As air circulates, the coated surfaces contact with the silver ions which can resist any airborne bacteria, which in turn suppress the respiration of bacteria, adversely affects bacteria's cellular metabolism and inhibits cell growth. Samsung maintain that the silver nano technology sterilizes over 650 types of bacteria and a “Samsung WM1245A Washing Machine releases over 400 billion silver ions which penetrate deeply into fabrics of any kind and create a coat of sterilizing protection for a maximum of 99.99% disinfection and an added antibacterial effect of up to 30 days after washing”.
There is an effort to incorporate silver nanoparticles, which have an antimicrobial effect that lasts longer than ionic silver, into a wide range of medical devices, including but not limited to bone cement, surgical instruments, surgical masks, wound dressings.
WO 2008/079149 A1 describes an antimicrobial formulation for dental applications that includes colloidal silver, from between about 0.01 to 2%, and colloidal copper, from between about 0.05 to 10%.
WO 2008/147395 A2 claims a solid or a foamed rubber, synthetic rubber, or neoprene, or other suitable polymer compound containing nanoparticles of at least one metal or metal compound comprising silver, gold, palladium, platinum and copper.
WO 2008/024422 A2 discloses incorporation of colloidal silver in compositions for use in partially or fully decontaminating surfaces which have been contaminated with chemical or biological warfare agents as well as to methods for treating viral infections, bacterial infections, fungal infections, and cancerous tissue.
WO 2008/033206 A1 is drawn to disinfectant compositions, which are human safe, that is food grade or food safe that may contain colloidal silver.
EP 2 018 839 A1 discloses preservative compositions with 0.1 to 1 ppm electrolytic silver for cosmetic products.
US 2009/0013825 A1 to provide a simple preparation method for silver nano particles having a well-controlled size in a surfactant solution. The nano silver colloid is prepared by the following step-wise procedure: (1) dissolving silver nitrate crystal in distilled water; (2) adding surfactant, LABS (Linear alkyl benzene sulfonate) to the solution and; (3) adding reducing agent to the solution. The preferred reducing agent is hydrazine.
US 2007/0009672 A1 describes a method for preparation of nanocomposite solution, comprising preparing basic silica colloid aqueous solution; providing an electrolysis apparatus by installing a negative electrode containing aluminum and a positive electrode containing silver into the basic silica colloid aqueous solution; and forming nanocomposite by applying voltage to the respective electrodes of the electrolysis apparatus. With this configuration, the present invention provides a method of manufacturing solution dispersed with nanocomposite, further particularly to, a method of manufacturing nanocomposite solution having excellent storability and thermal stability and containing silver having antibacterial function,
WO 2007/117087 A1 is drawn to provide a facilitated olefin transporting polymer membrane, which is capable of separating olefin and paraffin from each other using metal nanoparticles, in particular, silver nanoparticles, gold nanoparticles, or copper nanoparticles, as a carrier for facilitated transport.
WO 2008/024426 A2 provides hygienic absorbent articles, such as feminine sanitary napkins, tampons and disposable diapers, having antimicrobial activity that can minimize odors caused by body fluids. The articles of the invention include an absorbent member such as an elongated absorbent portion or pad that contains an antibacterial amount of substantially immobilized nanosilver particles or particles containing silver ions, preferably encased in a granule of a soluble carrier such as dextran, and the like, or a water-insoluble, but water-swellable superabsorbent polymer.
WO 20081100163 relates to a method of manufacturing silver nanoparticles, cellulosic fibers and nanofibers containing silver nanoparticles, fibers and nanofibers containing silver nanoparticles, use of silver nanoparticles to the manufacture of cellulosic fibers and nanofibers, and wound dressing containing silver nanoparticles.
WO 2008/147427 A2 A colorless composition comprising silver particles and water is disclosed. The particles have an interior of elemental silver and an exterior of ionic silver oxide, wherein the silver particles are present in the water at a level of about 5-40 ppm A preferred embodiment of the invention is a silver composition comprising particles of silver wherein more than 50% of the particles are less than 0.015 micrometers in size and the particles are colloidally suspended in water.
The composition manifests significant antiviral properties and is effective against avian influenza virus. Methods of use of the composition are described.
WO 2009/036714 A1 discloses is a composition for the treatment of wounds, containing hyaluronic acid, urea, and colloidal silver.
EP 2 027 956 A1 relates to a method for producing gold colloid including a nucleation
step of forming nuclear colloidal particles by adding a first reducing agent to a first gold salt solution; and a growth step of growing nuclear colloid by adding a second gold salt and a second reducing agent to the solution of the nuclear colloidal particles, characterized in that the growth step is performed at least once; a citrate is used as the first reducing agent and an ascorbate is used as the second reducing agent; and the addition of the ascorbate in the growth step is performed simultaneously with addition of the second gold salt.
Prior art describes the preparation and use of colloidal forms of noble metals, in particular colloidal silver, as biocides in various applications. Particle size and particle size distribution are often described as important properties of such colloidal dispersions although their values are rarely specified. In some prior art it is stated that it is desirable that at least 50% of the particle sizes have a particle size smaller than 15 nanometers. When nano-particles of noble metals are used as biocides only the metal atoms at the surface of the particles are able to come into contact with and interact with microbes of different kinds. Metal atoms in the interior of the particles have no access to the environment outside of the particles and therefore have no biocidal activity. Let ns and nt denote the number of surface atoms and the total number of atoms, for instance noble metal atoms, respectively. The ratio ns/nt is called the degree of dispersion of the noble metal and is a very important property of noble metals in applications, for instance many catalytic applications or biocidal applications, where their performance depend on the number of atoms they expose to their environment. The degree of dispersion decreases rapidly with particle size. In the case of for instance nano-particles of silver, the degree of dispersion thus decreases from about 85% to about 30% when the particle size grows from 1 nanometer to 5 nanometers. The degree of dispersion of 15 nanometer particles is less than 10%, indicating that more than 90% of the metal resides inactive in the interior of the particles.
Prior art also describes the use of ions of noble metals as biocides. One might say that the ions of for instance silver salts in aqueous solutions are perfectly dispersed; in such solutions the degree of dispersion of the noble metals is 100% as it were, but they may also be removed, for instance by leaching, from places where their biocidal function is needed and end up in places where their biocidal function is unwanted.